Composite Poly (Aryl Ether Ketone) Membranes, Their Preparation And Use Thereof

ABSTRACT

Disclosed is the preparation of composite membranes formed by a tailored selective chemical modification of an ultra-thin nanoporous surface layer of a semi-crystalline mesoporous poly (aryl ether ketone) membrane with graded density pore structure. The composite separation layer is synthesized in situ on the poly (aryl ether ketone) substrate surface and is covalently linked to the surface of the semi-crystalline mesoporous poly (aryl ether ketone) membrane. Hollow fiber configuration is the preferred embodiment of forming the functionalized the poly (aryl ether ketone) membranes. Composite poly (aryl ether ketone) membranes of the present invention are particularly useful for a broad range of fluid separation applications, including organic solvent ultrafiltration and nanofiltration to separate and recover active pharmaceutical ingredients.

FIELD OF THE INVENTION

This invention relates to the preparation and use of composite polymericmembranes for a broad range of fluid separations, and more particularly,to the preparation of such composite polymeric membranes formed bychemical functionalization of a porous poly (aryl ether ketone)substrate.

BACKGROUND OF THE INVENTION

Porous polymeric membranes are well known in the art and are used widelyfor filtration and purification processes, such as filtration of wastewater, desalination, preparation of ultra-pure water and in medical,pharmaceutical or food applications, including removal ofmicroorganisms, dialysis and protein filtration. A membrane is generallydefined as a selective barrier that permits passage of one or morecomponents through the membrane while retaining one or more components.Porous polymeric membranes are used to separate components of liquidmixtures by filtration, membrane distillation and as contactors tofacilitate dissolution of gases in liquids or to remove gases fromliquids, as membrane bioreactors, and in numerous other applicationswhere they serve as a generic phase separator, for example, as a batteryseparator. The application spectrum of membrane processes stretches fromfiltration of solids up to separations in a molecular range. Pressuredriven membrane processes, such as microfiltration (MF), ultrafiltration(UF), nanofiltration (NF) and reverse osmosis (RO), are establishedlarge scale industrial processes for water purification and recovery ofhigh value substances. Initially applied to water-based systems,membrane separations are increasingly applied to non-water solvent-basedsystems as well.

Composite polymeric membranes that consist of a selective separationlayer superimposed on a porous support constitute an advanced class offluid separation membranes. Composite membranes are used in waterpurification and desalination and in gas separation applications, suchas natural gas treatment, gas dehydration, and hydrogen recovery frompetrochemical and refinery streams. Most commonly used RO membranes arecomposite. The composite RO membrane consists of three layers: apolyester web, a microporous polysulfone interlayer support and anultra-thin polyamide barrier layer on the top surface formed by aninterfacial polymerization process. Composite membranes are furtherutilized for vapor permeation, removal of dissolved gases from liquidsand for dehydration of liquids. While these membranes have found broadutility for a variety of purposes, they suffer from severaldisadvantages: a broad and non-uniform pore size distribution, and alimited chemical, solvent and thermal resistance. This limits membraneutility in applications that require molecular level separations, suchas separation of active pharmaceutical ingredients, APIs. The synthesisof APIs is frequently carried out in aggressive solvent systems.Membranes capable of operation in aggressive chemical, solvent systemsat high temperatures while performing molecular level separations arethus needed.

Today's thin-film composite RO and NF membranes are made from polyamidesassembled on a porous support by interfacial polymerization. However,these membranes suffer from a low chemical stability, as the polyamidesare not stable in the presence of hypochlorite, which is commonly usedfor disinfection and membrane cleaning. Furthermore, these membranes aremostly produced in a flat sheet geometry and packed into spiral-woundmodules. Such modules cannot be cleaned by back washing, which is adesired strategy for membrane cleaning. The packing density of spiralwound modules is low as compared to hollow fiber membrane modules. Thus,there is a need for a composite membrane preparation methodologyapplicable to hollow fiber module configurations.

Membrane based fluid separations are pressure driven processes andconventionally classified by their ability to concentrate or purifymolecules based on molecular weight. Thus, ultrafiltration membranes areconventionally defined as separating molecules in the range of 10³-10⁶Da dissolved in solvents, in particular proteins. A nanofiltration (NF)membrane is classified as a pressure-driven membrane process, fallingbetween a reverse osmosis (RO) and ultrafiltration (UF) membrane. It haspore size in the range of 0.2-2 nm with molecular weight cut-off (MWCO)from 200 to 1000 Da. An organic solvent reverse osmosis process, OSRO,is defined as separating molecules below 200 Da dissolved in solvents.

Both pore size and functionality determine membrane separationefficiency. Membrane surface functionalization is a known method oftailoring membrane performance. The surface modification can be carriedout by wet chemistry reactions, grafting, including photopolymerization,and energetic methods, like plasma treatment, among others.

Commercial porous membranes are fabricated almost exclusively bysolution-based processes that limit their solvent and thermal resistanceand thus limit the scope of their application. Preparation of nanoporousmembranes from high temperature thermoplastics on a commercial scale bymelt processing is virtually unknown. The poly (aryl ether ketones) arepolymeric materials with exceptional thermo-mechanical properties andchemical/solvent resistance. It is an object of the instant invention todevelop a commercially scalable method of forming porous membranes withnanometer size pores from poly (aryl ether ketone) polymers and applythese membranes for fluid separation processes.

Preparation of porous membranes from poly (aryl ether ketones) has beenlimited to the family member poly (ether ether ketone), PEEK. A numberof methods to prepare porous PEEK membranes have been disclosed in theart. It is known to prepare porous PEEK membranes from solutions ofstrong acids, such as concentrated sulfuric acid. However, PEEK canundergo sulfonation in the concentrated sulfuric acid media and thus canlose some of its desirable sought after properties. U.S. Pat. No.6,017,455 discloses preparation of non-sulfonated porous PEEK membranesfrom concentrated sulfuric acid solvents sufficiently diluted by waterto prevent sulfonation. The membranes are formed by casting PEEKsolution to form a film followed by coagulation in a concentratedsulfuric acid. This membrane preparation process is complicated andproduces large amounts of waste acid.

U.S. Pat. No. 5,997,741 discloses preparation of porous PEEK membranesby forming a solution of PEEK polymer in a concentrated sulfuric acid atthe temperature of 15° C. or lower to prevent sulfonation. The solutionis processed and cast at a sub ambient temperature, followed bycoagulation in water or in a concentrated sulfuric acid. Only dilutePEEK solutions can be formed in the concentrated sulfuric acid, whichadversely affects film forming characteristics, the mechanicalcharacteristics, and the pore morphology of the thus formed porous PEEKmembranes.

U.S. Pat. Nos. 4,992,485 and 5,089,192 disclose preparation of porousPEEK membranes from non-sulfonating acid solvents, which include methanesulfonic acid and trifluoromethane sulfonic acid. European PatentSpecification EP 0737506 A1 discloses preparation of improved polymericmembranes based on PEEK admixtures with polyethylene terephthalate. Themembranes are formed by the solution casting process from a methanesulfuric acid/sulfuric acid solvent mixture.

The acid based solvent systems for manufacture of porous PEEK membranesdisclosed in the art are highly corrosive, frequently toxic and generatesubstantial environmental and disposal problems. For these and otherreasons, the acid based casting processes have found limited commercialuse.

An alternative to the acid based solvent system for PEEK membranepreparation involves the use of high boiling point solvents andplasticizers that dissolve PEEK polymer at elevated temperatures. U.S.Pat. Nos. 4,957,817 and 5,064,580, both issued to Dow Chemical Co.,disclose preparation of porous PEEK articles from its admixture withorganic polar solvents having a boiling point in the range of 191° C. to380° C., such as benzophenone and 1-chloronaphthalene, and organicplasticizers capable of dissolving at least 10 weight percent of PEEK,respectively. The final porous article is formed by removing the organicpolar solvents and/or plasticizers by dissolution into a low boilingtemperature solvent. U.S. Pat. No. 5,200,078 discloses preparation ofmicroporous PEEK membranes from its mixtures with plasticizers whereinthe membrane undergoes a drawing step prior to or after the plasticizeris removed by leaching. U.S. Pat. No. 5,227,101 issued to Dow ChemicalCo. discloses preparation of microporous membranes from poly(aryl etherketone) type polymer by forming a mixture of PEEK type polymer, a lowmelting point crystallizable polymer, and a plasticizer, heating theresulting mixture, extruding or casting the mixture into a membrane,quenching or coagulating the membrane and leaching the pore formingcomponents. U.S. Pat. No. 5,205,968, issued to Dow Chemical Co.,discloses preparation of microporous membranes from a blend containing apoly (aryl ether ketone) type polymer, an amorphous polymer and asolvent.

M. F. Sonnenschein, in the article entitled “Hollow fibermicrofiltration membranes from poly (ether ether ketone)”, published inthe Journal of Applied Polymer Science, Volume 72, pages 175-181, 1999,describes preparation of PEEK hollow fiber membranes by a thermal phaseinversion process. The use of a leachable additive polymer, such aspolysulfone, is proposed to enhance membrane performance. Preparation ofporous PEEK membranes by coextrusion of PEEK with polysulfone polymersfollowed by the dissolution of the polysulfone polymer from theinterpenetrating network is disclosed in European Patent Application EP0409416 A2.

It is also known in the art to prepare porous PEEK membranes from itsblends with a compatible poly (ether imide) polymer, PEI. Preparation ofsuch membranes is described by R. S. Dubrow and M. F. Froix in U.S. Pat.No. 4,721,732 and by R. H. Mehta et al. in an article entitled“Microporous membranes based on poly (ether ether ketone) via thermallyinduced phase separation”, published in the Journal of Membrane Science,Volume 107, pages 93-106, 1995. The porous structure of these PEEKmembranes is formed by leaching the poly (ether imide) component with anappropriate strong solvent such as dimethylformamide. However, asdescribed by Mehta et al., the quantitative removal of PEI component byleaching is essentially impossible which in turn can lead to an inferiorporous structure.

Japan Kokai Tokkyo Koho 91273038 assigned to Sumitomo ElectricIndustries, Ltd., discloses preparation of porous PEEK membranes by anion track etching method.

M. L. Bailey et al., in U.S. Pat. No. 5,651,931, describe a sinteringprocess for the preparation of biocompatible filters, including PEEKfilters. The filters are formed from a PEEK powder of a pre-selectedaverage particle size by first pressing the powder into a “cake”followed by sintering in an oven or furnace. The process is limited topreparation of filters with a relatively large pore size and a broadpore size distribution and does not provide economic means of forminglarge membrane area fluid separation devices.

A process for preparation of porous PAEK articles that preserves thedesirable thermal and chemical characteristics of PAEK polymers has beendisclosed in U.S. Pat. No. 6,887,408. The porous articles are preparedfrom PAEK blends with compatible polyimides. An article of targetedshape is formed from the PAEK/polyimide blend by melt processingfollowed by removal of the polyimide phase by reaction with a primaryamine. The method enables preparation of shaped porous PEEK articles,including hollow fibers membranes. Preparation of such hollow fibermembranes is described by Yong Ding and Ben Bikson in article entitled“Preparation and characterization of semi-crystalline poly (ether etherketone) hollow fiber membranes”, published in the Journal of MembraneScience, volume 357 (2010), p. 192-198. Preparation of hollow fibermembranes by this methodology is further described by Gong Chen, YuanChen, Tingjian Huang, Zhongchen He, Jianjun Xu and Pengqing Liu, in thearticle entitled “Pore Structure and Properties of PEEK Hollow FiberMembranes: Influence of the Phase Structure Evolution of PEEK/PEIComposite”, Polymers, Volume 11 (2019), p. 1398.

D. Morrisette and P. Croteu, in PCT application, InternationalPublication Number WO2007/051309, disclose porous PEEK material suitablefor medical implant devices. The porous material is formed by mixingdissolvable material with PEEK in a molten form and subsequentlyremoving the dissolvable material. The disclosed dissolvable material isa salt. The method capable of forming PEEK materials with very largepore size and irregular pore structure.

M. C. Iliuta et al., in U.S. Pat. No. 9,908,985, disclose preparation ofmicroporous hydrophobic polymeric hollow fibers. The hollow fibers areprepared by melt processing from mixture of polymer with micron sizeNaCl particles followed by salt dissolution. The hollow fiber isreported to be non-wetting and useful for gas transfer contactingapplications.

Poly (aryl ether ketones) are high performance engineering polymers thatexhibit exceptional thermal and chemical characteristics and are thushighly sought after as porous substrates for applications that requiresolvent and thermal resistance. However, the properties that make PAEKpolymers desirable also make preparation of porous media difficult. Incontrast, the chemical resistance of PAEK polymers enables chemicalmodification of preformed polymer surfaces without alteration of theunderlying structure.

Surface functionalization of PEEK articles is of great interest. Thework to date has largely been limited to surface functionalization ofsolid PEEK articles. The poly (aryl ether) backbone structure of PEEKprovides for unique methodologies of surface functionalization viaketone group modification using wet chemistry methodologies. The mostfrequently utilized method of PEEK functionalization is via reduction ofsurface ketone groups to form hydroxyl group functionalized surfaces.The preparation of —OH group functionalized dense PEEK materials isdescribed by O. Noiset et al., in Macromolecules, 30, (1997), 540; andby 0. Noiset, et al. in J. Biomat. Sci., Polymer Ed., 11, (2000),767-786, DOI: 10.1163/156856200744002. The preparation of —OH groupfunctionalized dense PEEK materials is further described by A.Diez-Pascual, et al., in Macromolecules., 62, (2009), 6885. The surfacesof dense PEEK materials have been further functionalized with aminogroups, carboxyl groups and amino acid groups among others. Thesefunctionalization methodologies are described in the followingpublications: O. Noiset, et al. Polym. Sci.: Part A: Polym. Chem., 35,(1997) 3779-3790; C. Henneuse-Boxus, E. Duliere and J.Marchand-Brynaert, Europ. Polym. J., 37 (2001) 9-18; C. Henneuse-Boxus,et al. Polym., 39 (1998) 835-844; C. Henneuse-Boxus, et al. Polymer, 39(1998) 5359-5369.

Surface functionalization of porous PEEK membranes to impart hydrophobiccharacteristics is described in U.S. Pat. Nos. 9,610,547 and 10,376,846entitled “Composite perfluorocarbon membranes, their preparation anduse”. The porous PEEK is first functionalized with hydroxyl groups thatare further reacted with functional hydrophobic molecules.Functionalization of porous poly (aryl ether ketone) articles byreacting ketone groups in the backbone of poly (aryl ether ketone)polymer with a primary amine reagent are disclosed in U.S. Pat. Nos.7,176,273 and 7,368,526.

In view of these, and other, advantageous properties associated withPAEK polymers, and to build on the previously known uses of suchpolymers, it would be desirable to provide a commercially feasiblemethod for preparing composite polymeric membranes formed by chemicalfunctionalization of a porous poly (aryl ether ketone) substrate, alongwith systems and methods employing such composite polymeric membranesfor a broad range of fluid separations.

SUMMARY OF THE INVENTION

Disclosed is the preparation of composite poly (aryl ether ketone),PAEK, membranes and their use for a broad range of fluid separationapplications. The composite membrane consists of an ultra-thinnanoporous separation layer supported by a porous PAEK substratecontaining larger size pores. The separation layer can further containtarget functional groups covalently attached to the asymmetric PAEKsubstrate. In this regard, the present invention takes advantage of thesurprising discovery that composite poly (aryl ether ketone) membraneswith an ultra-thin separation layer containing nanometer size pores canbe formed utilizing porous poly (aryl ether ketone) substratescontaining an asymmetric pore structure (smaller size surface pores andlarger diameter interior size pores). The nanoporous separation layercan be further modified with target functional groups without affectingpre-formed interior porous structure. Such composite PAEK membranes areused for a broad range of fluid separation processes.

The nanoporous membranes of this invention are comprised of a poly (arylether ketone) or a blend of poly (aryl ether ketone)s. The preferredpoly (aryl ether ketone)s are poly (ether ether ketone), PEEK, poly(ether ketone), PEK, poly (ether ketone ketone), PEKK, and poly (etherketone ether ketone ketone), PEKEKK, as well as their copolymers. Thepoly (aryl ether ketone)s are manufactured by Victrex Corporation underthe trade names Victrex® PEEK, Victrex® PEEK HT, and Victrex® PEEK ST.Poly (ether ether ketone) is further available from Solvay under tradename KetaSpire™ and another poly (aryl ether ketone) is available fromSolvay under the trade name AvaSpire®. Poly (ether ether ketone) isfurther available from Evonik under the trade name VESTAKEEP®.

In one embodiment of the instant invention, an asymmetric surfacefunctionalized poly (aryl ether ketone) fluid separation membrane isformed by a multi-step process: (a) a solid (non-porous) precursorarticle of a desired shape is formed from a poly (aryl ether ketone)polymer blend with a pore forming material, (b) benzophenone segments ofpoly (aryl ether ketone) polymer on only the surface of the precursorshaped article are modified with functional groups, and (c) the solidpoly (aryl ether ketone) precursor article is converted into ananoporous membrane by removing the pore forming material. Preferredfunctional groups are selected from primary, secondary, tertiary orquaternary amine groups, carboxyl group, sulfonic acid group, phosphategroup, primary, secondary or tertiary hydroxyl groups and/or sulfhydrylgroup. In some embodiments, the shaped article undergoes crystallizationvia sequence of solvent and thermal treatments following step (a). Thetreatment leads to formation of PAEK substrate with an asymmetric porestructure. Alternatively, the article undergoes crystallization aftersurface modification step (b). The preferred article shape is the hollowfiber configuration and the preferred pore forming material ispolyetherimide.

In another embodiment of the instant invention, the asymmetric surfacefunctionalized poly (aryl ether ketone) fluid separation membrane isformed by a multi-step process: (a) a solid (non-porous) precursorarticle of a desired shape is formed from a poly (aryl ether ketone)polymer blend with a pore forming material, (b) the surface of the solidpoly (aryl ether ketone) precursor article is converted into a thinnanoporous layer by removing the pore forming material from the surfaceof the article to a predetermined depth, (c) the thus formed mesoporouslayer is modified with functional groups via chemical modification ofbenzophenone segments of poly (aryl ether ketone) polymer, and (d) thesolid poly (aryl ether ketone) precursor article is converted into ananoporous composite membrane by removing the remaining pore formingmaterial. In some embodiments of the invention, steps (b) and (c) takeplace simultaneously. It is within the scope of the invention tocrystallize the article via sequence of solvent and thermal treatmentsfollowing step (a). The preferred article shape is the hollow fiberconfiguration and the preferred pore forming material is polyetherimide.Preferred functional groups are selected from primary, secondary,tertiary or quaternary amine groups, carboxyl group, sulfonic acidgroup, phosphate group, primary, secondary or tertiary hydroxyl groups,ethylene oxide groups and/or sulfhydryl group.

In another embodiment of the instant invention, the asymmetric surfacefunctionalized poly (aryl ether ketone) fluid separation membrane isformed by a multi-step process: (a) a solid (non-porous) precursorarticle of a desired shape is formed from a poly (aryl ether ketone)polymer blend with a pore forming material, (b) the article is subjectedto a treatment step wherein poly (aryl ether ketone) polymer undergoescrystallization, (c) the solid poly (aryl ether ketone) precursorarticle is converted into a nanoporous substrate by removing the poreforming material, (d) the nanoporous membrane is formed by modifying thesubstrate with functional groups. Preferably, the crystallization of thepoly (aryl ether ketone) polymer in the blend during step (b) is carriedout via sequence of solvent and thermal treatments. The treatment leadsto formation of PAEK substrate with an asymmetric pore structure. Thepreferred article shape is the hollow fiber configuration and thepreferred pore forming material is polyetherimide. Preferred functionalgroups are selected from primary, secondary, tertiary or quaternaryamine groups, carboxyl group, sulfonic acid group, phosphate group,primary, secondary or tertiary hydroxyl groups, ethylene oxide and/orsulfhydryl group.

In one example, a mesoporous precursor article is prepared from a blendof PAEK polymer with a pore forming material (porogen). A precursornon-porous article is prepared from the PAEK/porogen blend by meltprocessing and is initially amorphous. The precursor amorphous articleundergoes crystallization by subjecting the article to a solventtreatment step. The solvent and the treatment conditions are selected toaffect crystallization of PAEK polymer phase in the article. Thecrystallization by the solvent treatment can be limited to the surfaceregion of the article only. The solvent treatment step can be furtherfollowed by a thermal annealing step to affect crystallization of theinterior. This sequential crystallization process leads to formation ofthe asymmetric pore structure in the PAEK substrate following porogenremoval. The porogen acts as a pore forming material and is removedfollowing the crystallization step to provide the initial asymmetricporous PAEK substrate article. The porous surface of the article ismodified by functional groups to form the fluid separation membrane. Insome embodiments, the surface functionalization is carried out followingthe thermal annealing step and prior to the porogen removal step. Insome embodiments, the surface functional groups are further reacted withextender groups to modify pore size and membrane surfacecharacteristics.

In one preferred embodiment, the surface functional groups are formed bya wet-chemical surface modification of the pre-formed shaped PAEKarticle that serves as a substrate. The PAEK substrate surface ismodified with amino, carboxyl, acid chloride, aldehyde, isocyanate,sulfhydryl or hydroxyl functional groups that are particularlypreferred. It is within the scope of the invention to covalently attachextender groups to the surface functional groups to further affect poresize and functionality. In this step, the functionalized porous PAEKsubstrate is reacted with a functional monomer that forms a brushextender group. The brush extender molecules modify the surface poresize to affect the separation efficiency. Brush extenders include lowmolecular weight hydrocarbons, oligomers or polymers containingfunctional groups, such as epoxy group or primary amino-groups ˜NH₂,wherein one set of functional groups is used to attach the brush to thefunctionalized poly (aryl ether ketone) surface. The attachment of thefirst targeted multi-functional extender group molecules can be followedby reacting the thus formed layer with an additional set of brushextender molecules to further affect pore size.

The PAEK precursor substrate used to form the composite membrane of thisinvention preferably exhibits a nanoporous surface pore structure with anarrow pore size distribution and an average surface pore size between 5and 100 nanometers, preferably between 10 and 30 nm, and the interiorpore size that is larger than the surface pore size by a factor of twoor more. The substrate is pre-shaped as a film, a hollow fiber, a fritor a monolith. In some embodiments, the interior porous structure of themembrane exhibits a bimodal pore size distribution. The bimodaldistribution consists of a mesoporous pore fraction with an average poresize below 50 nanometer and a macro-porous pore fraction with an averagepore size above 0.5 micron.

In some embodiments, the fluid separation membrane is prepared by amethod comprising: (a) forming a blend of poly(aryl ether ketone)polymer with a polyimide; (b) forming a shaped article from the blend byextrusion, casting or molding; (c) annealing the shaped article; (d)forming a porous structure throughout the shaped article, whilesimultaneously functionalizing the surface of the shaped article bybringing the article into contact with a primary amine to simultaneouslydecomposing the polyimide in the shaped article into low molecularweight fragments and functionalizing its surface, and (e) removing thelow molecular weight fragments from the article.

In another example, the fluid separation membrane is prepared by amethod comprising: (a) forming a blend of poly(aryl ether ketone) typepolymer with a polyimide; (b) forming a shaped article from the blend byextrusion, casting, or molding; (c) crystallizing a fraction ofpoly(aryl ether ketone) polymer in the shaped article; (d) bringing theshaped article into contact with a primary amine to affect decompositionof the polyimide in the shaped article into low molecular weightfragments under conditions that do not cause functionalization of thepoly(aryl ether ketone) polymer with the primary amine; (e) removing thelow molecular weight fragments from the article; and (f) drying theporous poly(aryl ether ketone) article. The precursor amorphous articleundergoes crystallization by subjecting the article to a solventtreatment step first followed by a thermal treatment. The solvent andthe treatment conditions are selected to affect crystallization of PAEKpolymer phase in the article in sequential steps. The crystallization bythe solvent treatment is limited to the surface region of the articleonly. The solvent treatment step is further followed by a thermalannealing step to affect crystallization of the interior. Thissequential crystallization process leads to formation of the asymmetricpore structure in the PAEK substrate following polyimide phase removal.The porous PAEK substrate formed by the above-described process isfunctionalized in a subsequent step with target surface groups. The thusformed membrane is incorporated into a fluid separation device. In someembodiments, the functionalization step is carried out in-situ in thefluid separation device.

The composite membranes of this invention separate components of fluidmixtures by selective permeation. The fluid mixture may contain multipledissolved components. The fluid mixture is separated into a fractionenriched in at least one dissolved component and a fraction depleted inthis dissolved component by permeation through composite membrane. Theseparation process is carried out by bringing the fluid mixture intocontact with the composite fluid separation membrane while a pressuredifference is maintained across the membrane, or in the case of a vaporcomponent, a partial pressure difference is maintained across themembrane. The membrane separation layer formed on the surface of a poly(aryl ether ketone) membrane is in direct contact with the feed fluidmixture. A fraction enriched in the dissolved component and a fractiondepleted in the dissolved component are generated by preferentiallypermeating a portion of the fluid mixture through the composite fluidseparation membrane.

The fluid separation membranes of the present invention are particularlyuseful for separation of components dissolved or suspended in organicsolvent media. PAEK membranes are solvent resistant and can be used totreat a broad range of solution of organic solvents including aromatic,heterocyclic and aliphatic hydrocarbons, ketones, aprotic solvents,alcohols and chlorinated solvents. The pore size and functionality ofthe separation layer is tailored to a specific separation application.The separation of dissolved molecules with molecular weight above 1000Da is referred to as organic solvent ultrafiltration, OSUF, separationof molecules with molecular weight in the 200-1000 Da range is referredto as organic solvent nanofiltration, OSNF, and separation of moleculeswith molecular weight below 200 Dalton is referred to as an organicsolvent reverse osmosis, OSRO, process.

The method of the invention provides for separation of a fluid mixtureinto a fraction enriched in at least one dissolved component and afraction depleted in this dissolved component by bringing the fluidmixture in contact with a composite poly (aryl ether ketone) membranewhereby a fraction enriched in the dissolved component and a fractiondepleted in the dissolved component are generated by preferentiallypermeating a portion of organic fluid mixture through the fluidseparation membrane The fluid mixture is brought in contact with PAEKbased fluid separation membrane while maintaining a pressure difference,or in case of a vapor component a partial pressure difference, acrossthe membrane. The PAEK membrane has a separation layer formed on thesurface of the PAEK membrane via chemical modification of benzophenonesegments of the polymeric backbone.

The composite PAEK membranes of this invention can address a broad rangeof well-established fluid separations, including ultrafiltration (UF),nanofiltration (NF) and reverse osmosis (RO) processes. Emergingapplications, such as organic solvent nanofiltration and the separationand recovery of active pharmaceutical ingredients, can be furtherefficiently addressed by membranes of this invention.

The above and other features of the invention, including various noveldetails of construction and combinations of parts, and other advantages,will now be more particularly described and pointed out in the appendedclaims. It will be understood that the particular methods and devicesembodying the invention are shown by way of illustration and not as alimitation of the invention. The principles and features of thisinvention may be employed in various and numerous embodiments withoutdeparting from the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show, respectively, AT-FTIR spectra of an original PEEKhollow fiber and a PEEK-OH hollow fiber reduced with NaBH₄ for 3 hours.

FIG. 2 illustrates red carbo-cation formation by PEEK-OH dissolved inconcentrated sulfuric acid.

FIGS. 3A and 3B show UV-VIS spectra of PEEK-OH hollow fiber dilutesolution in sulfuric acid, with FIG. 3A showing PEEK-OH and precursorPEEK at identical concentration measured against pure sulfuric acid, andwith FIG. 3B showing PEEK-OH measured against precursor PEEK atidentical concentrations in sulfuric acid.

FIG. 4A shows a UV-VIS spectra of modelcompound-bis(4-(4-methoxyphenoxy)phenyl)methanol, BMPPM in sulfuricacid, while FIG. 4B shows a corresponding calibration curve using theabsorption peak at 508 nm.

FIGS. 5A and 5B show microphotographs of a hollow fiber cross sectionwith a porous exterior surface layer and dense non-porous interior wall,with FIG. 5A showing a SEM microphotograph of the hollow fiber crosssection, and FIG. 5B showing a cross section of hollow fiber with eosindye staining of the exterior porous layer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Disclosed is a method for conducting fluid separations using compositepoly (aryl ether ketone), PAEK, membranes. Also disclosed is thepreparation of composite nanoporous PAEK hollow fiber membranes withtailored ultra-thin functionalized surface layers and their use forfluid separation processes. More particularly, the teachings of thepresent invention are directed to the preparation of solvent resistantnanoporous composite PAEK hollow fiber membranes with an asymmetric wallpore structure and functionalized separation layer and their use forultra-filtration, nanofiltration and reverse osmosis processes.

Separation processes of the instant invention are characterized by theuse of a composite porous PAEK membrane with an ultra-thinfunctionalized surface separation layer. The porous membrane can be inthe form of a flat sheet, frit, monolith or hollow fiber. In thepreferred embodiment, the porous PAEK membrane is a nanoporous hollowfiber membrane. A method of the instant invention separates a fluidmixture into a fraction enriched in a least one dissolved component anda fraction depleted in the dissolved component by contacting the fluidmixture with a first side of the fluid separation membrane whilemaintaining a pressure difference, or in case of a vapor component apartial pressure difference, across the membrane, whereby a fractionenriched in the dissolved component and a fraction depleted in thedissolved component are generated by preferentially permeating a portionof the fluid mixture through the fluid separation membrane, and wherebythe fraction depleted in the dissolved component is collected as apermeate from the second side of the membrane. The porous membrane isformed from a poly (aryl ether ketone) polymer with the membraneseparation layer formed by chemical modification of ketone groups in thebenzophenone segments of the polymeric backbone. In some embodiments thepore surface across the entire cross section of the asymmetric membraneis functionalized by chemical modification of ketone groups in thebenzophenone polymer backbone.

Membranes used in fluid separation processes of this invention arecomposite poly (aryl ether ketone), PAEK, membranes. The surface of PAEKsubstrate used in composite membrane preparation exhibits a uniform,narrow pore size distribution. The pore size is substantially within themesoporous size range. A mesoporous material is a material containingpores with diameters between 2 and 50 nm, according to the InternationalUnion of Pure and Applied Chemistry, IUPAC, nomenclature. Forcomparison, IUPAC defines microporous material as a material havingpores smaller than 2 nm in diameter and macroporous material as amaterial having pores larger than 50 nm in diameter. The porous PAEKsubstrates used for preparation of composite membranes exhibit anaverage pore diameter between 5 and 100 nm which is defined herein asbeing substantially mesoporous or nanoporous. In some embodiments ofthis invention, the porous structure of the PAEK substrate is composedof structural segments that differ in pore size; this includes poroussubstrates composed of two or more layers of different pore sizes. Thelayers can contain mesopores that differ in pore size. The substrate'sinterior can be composed of mesoporous and macroporous layers or exhibita bimodal pore distribution that contain mesopores and macropores.Preferably, the average interior pore diameter of the membrane is largerthan the average diameter of surface pores by a factor of two or more.

The nanoporous membranes used in the methods of the present inventionare formed from poly (aryl ether ketone), PAEK, polymers. The porouspoly (aryl ether ketone) polymers are defined as polymers containing atleast one repeat aryl ether ketone segment in the polymeric backbone. Anumber of poly (aryl ether ketone) polymers are available commerciallyincluding poly (ether ketone), poly (ether ether ketone), poly (etherketone ketone), poly (ether ether ketone ketone), poly (ether ketoneether ketone ketone) and copolymers collectively referred herein as poly(aryl ether ketones). Poly (aryl ether ketones) have an averagemolecular weight in the range of 20,000 to 1,000,000 Daltons, typicallybetween 30,000 to 500,000 Daltons. Preferred poly (aryl ether ketones)used to form porous PAEK membranes of this invention aresemi-crystalline, and are insoluble in common organic solvents at roomtemperature. Most preferred poly (aryl ether ketones) used to formporous PAEK articles of this invention are poly (ether ether ketone),PEEK, poly (ether ketone), PEK, poly (ether ketone ketone), PEKK, poly(ether ether ketone ketone), PEEKK, and poly (ether ketone ether ketoneketone), PEKEKK. A number of poly (aryl ether ketones) are manufacturedby Victrex Corporation under the trade names Victrex® PEEK, Victrex®PEEK HT, and Victrex® PEEK ST. Poly (ether ether ketone) is furtheravailable from Solvay under trade name KetaSpire™ and another poly (arylether ketone) is available from Solvay under the trade name AvaSpire®.Poly (ether ether ketone) is further available from Evonik Corporationunder the trade name VESTAKEEP®.

The PAEK substrate used in preparation of composite fluid separationmembranes of this invention can be in a flat sheet configuration, in theform of a monolith, frit or in a hollow fiber (micro capillary)configuration wherein membrane configurations exhibit a nanoporous poresurface structure with a narrow pore size distribution and an averagesurface pore size between 5 and 100 nanometers. The membrane ispreferably shaped as a hollow fiber. In some embodiments, the membranewall structure exhibits a bimodal pore size distribution. The bimodaldistribution consists of a mesoporous pore fraction with an average poresize below 100 nanometer and a macro-porous pore fraction with anaverage pore size above 0.5 micron. It is particularly preferred toutilize porous PAEK hollow fibers for fluid separation applications withasymmetric or multi-layer pore wall morphology. Hollow fibers withgraded pore structure composed of a thin mesoporous surface layer andmacro-porous bulk wall structure exhibit higher solute mass transferrates while maintaining good stability. Hollow fibers with the layeredgraded pore structure are formed by coextrusion processes from membraneforming compositions with different contents of pore forming materials.At least one layer of multilayer structure is asymmetric withsubstantially smaller size surface pores as compared to interior poresize. The porous surface of asymmetric and multilayer PAEK hollow fibersis functionalized via chemical modification of ketone group inbenzophenone segments of the polymeric backbone. In the preferredembodiment the exterior ultra-thin layer only is functionalized viachemical modification of benzophenone segments of the polymeric backboneto form a composite PAEK membrane.

The preferred method of forming the functionalized PAEK membrane is byfirst forming the PAEK substrate. The PAEK substrate is preferablyformed by melt processing. The preparation of the porous poly (arylether ketone) substrate typically consists of the following steps: (1)Forming a blend of poly (aryl ether ketone) polymer with a pore formingmaterial (porogen) by melt blending. The porogen is alternatively adiluent (a high boiling, low molecular weight liquid or solid), anintermediate molecular weight oligomer, a polymer or a mixture thereof;(2) Forming a shaped article from the blend by melt processing, such asextrusion, injection molding, casting, or molding; (3) Solidifying theshaped article by cooling; (4) Treating the article to affectcrystallization of the PAEK polymer component; (5) Removing the porogen(the porogen is typically removed by extraction or reactive extraction);and (6) Drying the porous PAEK substrate.

The crystallization rate of poly (aryl ether ketones) is relativelyslow. The crystallization rate of PAEK blends, in particular thePAEK/polyimide blends, can be further retarded. At high melt processingconditions such as extrusion the precursor shaped article is cooled downrapidly. These processing conditions retard crystallization and lead tothe formation of a substantially amorphous article. The article formedunder the rapidly cooling conditions may be thus substantiallyamorphous. Substantially amorphous article/substrate is defined as aPAEK article that did not attain a high optimal degree of crystallinity.For fully crystallized solid PAEK polymers, the degree of crystallinitycan reach up to 40%, with 35% representing an average degree ofcrystallinity. Substantially amorphous PAEK/blend articles formed bymelt processing exhibit a degree of crystallinity below 20%. Inpreferred embodiments the PAEK/blend articles exhibit a degree ofcrystallinity below 5%. The low initial degree of crystallinity enablesdevelopment of the desired semi-crystalline morphology via thesubsequent crystallization steps that may include a sequence of solventinduced crystallization followed by a thermally induced crystallization.

Prior to or subsequent to porogen removal from the substrate, thesubstrate can be treated to increase the degree of crystallinity of thePAEK phase by a thermal process or via solvent induced crystallization.Both methods are known in the art. The term annealing as defined hereinrefers to a processing step or condition that leads to an increase inthe degree of crystallinity of the PAEK phase. The annealing can takeplace during the solidification step through the control of coolingrate. For example, the annealing can be carried out in line during theextrusion step by controlling the cooling rate. Alternatively, or in anaddition, the annealing can be carried out in a subsequent step after anamorphous article has been formed by rapid solidification. In the lattercase the solidified article can be placed in an oven or transportedthrough a heating zone for a period of time sufficient to affectcrystallization. The article can be annealed prior to the removal of theporogen to increase the degree of crystallinity of the PAEK phase at atemperature from about 150° C. to about 330° C., preferably from about200° C. to about 310° C., most preferably from 250° C. to about 310° C.

Solvent induced crystallization can be carried out utilizing solventsthat affect PAEK polymer crystallization. The solvent treatment can becarried out in an alcohol, a ketone, a chlorinated hydrocarbon,polyethylene glycol, an aromatic hydrocarbon or a mixture thereof. Thesolvent temperature can greatly affect the rate of crystallization. Thecombination of treatment temperature and the duration of the treatmentcan be used to control the depth of solvent induced crystallizationtreatment. The alcohols are selected from butanol, ethylene glycol,propylene glycol, isobutyl alcohol, tert-amyl alcohol, cetyl alcohol,pentanol, cyclohexanol or glycerol.

The ketones are particularly preferred and selected from acetone, methylethyl ketone (butanone), 2-hexanone, isophorone, methyl isobutyl ketone,cyclopentanone, acetophenone, valerophenone or pentanone. The solventtreatment can be carried out at an elevated temperature, but preferablybelow the boiling point of the solvent.

The annealing can take the form of a combination of solvent treatmentsteps followed by the thermal crystallization step. The crystallizationprotocol affects the crystalline morphology and crystal size that, inturn, affects pore structure. The pore volume is controlled byPAEK/porogen weight ratio in the blend and can range from 20/80 to60/40, but preferably the ratio can range between 35/65 and 50/50.

Pore forming additives (porogens) can include high boiling solvents,compatible oligomers, nanoparticles or compatible or semi-compatiblepolymers. The use of compatible polymers or their mixtures withpartially compatible polymers or nanoparticles as porogens is generallypreferred. Preferred polymeric porogens include polysulfones, such aspoly (ether sulfone), poly (ether ether sulfone), biphenol basedpolysulfones and bisphenol A based polysulfone, polycaprolactone,polyimides or mixtures thereof. The nanoparticles are soluble organic orinorganic materials. Inorganic nanoparticles, such as sodium chlorideand sodium carbonate, are preferred. The most preferred polymericporogens are aromatic polyimides. Poly (aryl ether ketone) type polymersform compatible blends with certain aromatic polyimides, Pls. Removal ofthe polyimide component from such blend articles by solvent extraction,however, can be difficult due to polymer chain entanglement. Thepolyimide can be quantitatively removed by selective chemicaldecomposition of the polyimide phase to form the final porous article.This method of porous PAEK material preparation is referred to as thereactive porogen removal process, RPR. In some embodiments a ternaryblend of PAEK/polysulfone/polyimide is utilized.

Polyimides that form a compatible precursor blend with poly (aryl etherketone) polymers are defined as polymers containing

linkages and include aliphatic and aromatic polyimides, copolyimides andpolyimide block and graft copolymers, wherein the polyimide is definedas a molecule that contains at least two imide linkages. Additionalpolyimides include aromatic polyamide imides, polyhydrazine imides andpolyester imides.

Aromatic polyimides are particularly useful for the preparation ofporous articles of this invention. The most preferred polyimide is poly(ether imide), PEI, of the following formula:

and poly (ether imide) copolymers manufactured by the Sabic Industriesunder trade names Ultem® 1000. Ultem® XH1010F, Ultem® 6050 and Siltem®STM1500. The copolymers that contain dimethylsiloxane or sulfone unitsare examples of representative copolymers. Another preferred polyimideis Aurum® manufactured by Mitsui and distributed by DuPont EngineeringPolymers.

The polyimides can be used as a single additive component or as amixture of polyimides. The polyimides typically have an averagemolecular weight in the range of 500 to 1,000,000 Daltons, preferablybetween 1,000 to 500,000 Daltons.

Mixtures of poly (ether imide) with poly (ether sulfone), PES, poly(ether ether sulfone), PEES, or polycaprolactone as well as PEI mixtureswith soluble nanoparticles are also within the scope of the presentinvention. The preferred soluble nanoparticles are salt nanoparticles,such as sodium chloride nanoparticles available from Nanoshel. Theadditional pore forming components supplement the PEI pore formingmaterial and augment pore structures formed from bicomponent PAEK/PEIblends. These supplemental additives are considered compatible PEIcomponents. PAEK substrates prepared from blends containing multiplepore forming components exhibit bimodal pore distributions that combinemesopores below 50 nanometer size with macropores above 0.1 micron size.The PAEK substrate with this combination of pore sizes can provide adecrease in pressure drop across the media in the flow thoughconfiguration. The PAEK polymer concentrations in blends containingmultiple pore forming components range from 20 to 60 percent by weight,while PEI/supplemental compatible component weight ratios in the multicomponent blends range from 20/80 to 80/20. Multicomponent compositionsformed from blends of PAEK with PEI and nanoparticles exhibit higherfluxes. The concentration of poly (aryl ether ketone) in thesemulticomponent blend composition ranges from 20 to 60 percent by weightand the nanoparticles weight ratios to the total amount of pore formingmaterials in the multi component blends range from 20/80 to 80/20.

The formation of the binary poly (aryl ether ketone) blend with thepolyimide or multicomponent blends can be carried out by mixingcomponents in a molten stage, such as by melt compounding, and othermethods conventionally employed in the polymer compounding industry. Theuse of a twin extruder is the preferred method of blending. Aplasticizer can be optionally added to aid processing. The poly (arylether ketone)/polyimide blends form compatible blend compositions. Thecompatible blend typically exhibits a single glass transitiontemperature. The compatible composition is defined as capable of formingmesoporous poly (aryl ether ketone) articles with inter-connected porestructure and majority fraction of pore volume having pore diameter inthe range of 5 to 100 nanometers. Preferred blends are PEEK/PEI blendsthat form poly (aryl ether ketone) articles with inter-connected porestructure and an average pore diameter of 50 nm or less. Themulticomponent PEEK/PEI/compatible additive blends that form poly (arylether ketone) articles with inter-connected pore structure and bimodalpore distribution with combination of meso and macro pores are alsopreferred. The mesopore diameter is below 50 nanometers while macroporediameter is in the range of 0.1 to 5 micron. The specific membraneseparation requirements determine the desired pore size and pore sizedistribution that in turn is determined by PAEK and polyimide selectionand by PAEK/PEI ratio. Incorporation of supplementary PEI competitiveadditives into blend compositions and downstream processing conditions,such as crystallization protocol, further affect PAEK substratemorphology and can be used to tailor porous structure towards thespecific composite membrane preparation.

Blends suitable for preparation of porous articles in accordance withthis invention comprise from about 20 to about 60 weight percent of thepoly (aryl ether ketone) polymer component, preferably from about 25 toabout 50 weight percent of the poly (aryl ether ketone) component, mostpreferably from 35 to 50 weight percent.

In addition to the supplemental PEI compatible additive compounds listedabove, blends can contain solvents to reduce blend viscosity,stabilizers, pigments, fillers, such as catalytic particles,plasticizers, and the like.

The poly (aryl ether ketone)/polyimide blends can be fabricated into aflat sheet film, a hollow fiber, a frit, a monolith or other desiredshape precursor substrates by melt extrusion, casting, compressionmolding or injection molding. The preferred membrane configuration isthe hollow fibers. The hollow fiber preferably possesses an outsidediameter from about 50 to about 1000 micrometers, more preferably fromabout 80 to about 500 micrometers, with a wall thickness from about 10to about 100 micrometers. In the case of films and frits, the mediathickness can fall within a broad range, the thickness being limited bythe pressure drop for the flow-through process configuration. Flat sheetfilms may be optionally supported by a non-woven material or by ascreen. The article configuration will depend on the intended use. Priorto polyimide phase removal, the article is preferably crystallized toattain the desired degree of crystallinity and crystalline morphology ofthe PAEK phase. As discussed above, the annealing can take place duringthe solidification step through control of the cooling rate or by asubsequent combination of solvent induced crystallization and thermaltreatment.

The removal of the polyimide component from the blend can be effectivelycarried out by the reactive porogen removal process, RPR, utilizingreagents that decompose the polyimide into low molecular weight easilyextractable fragments. The suitable classes of reagents include, but arenot limited to, ammonia, tetraalkylammonium hydroxides, hydrazine,alkylhydrazines, hydroxyalkylhydrazine, primary aliphatic amines, orsecondary aliphatic amines. In some embodiments, the reagent thataffects polyimide decomposition is diluted with a solvent and/orcontains water. Examples of suitable solvents include alcohols, ketones,hydrocarbons, water, and aprotic solvents such as NMP, DMF, and thelike. Amine reagents suitable to decompose the polyimide phase inaccordance with this invention include, but are not limited to, primaryand secondary amines, such as methylamine, ethylamine, propylamine,butylamine, ethylenediamine, propylenediamine, butylenediamine,morpholine, piperazine, monoethanolamine, ethylethanolamine,diethanolamine, propanolamine, dipropanolamine, and mixtures thereof.Commercially available amine mixtures, such as Ucarsol®, can be alsoemployed. The preferred amines include hydrazine, monoethanolamine,tetramethylammonium hydroxide, and their mixtures with alcohols, such asmethanol, ethanol, isopropanol, or butanol, ketones, water, and aproticsolvents. The most preferred reagents for the decomposition of thepolyimide phase are monoethanolamine, MEA, hydrazine andtetramethylammonium hydroxide.

The decomposition and removal of the polyimide component can be carriedout at an ambient temperature, but preferably is carried out at elevatedtemperatures to facilitate the decomposition process and the removal ofdecomposition products. Preferably, the polyimide decomposition processand the removal of the low molecular weight decomposition product arecarried out concurrently in a common solvent media. The comprehensiveremoval of decomposition products requires additional washing. In oneembodiment of this invention, the polyimide decomposition and removalprocess is carried out at temperature from about 50° C. to about 180°C., preferably from about 80° C. to 150° C. The time required to fullydecompose polyimide and to remove products of the decomposition processfrom the article will depend on the shape, crystalline morphology, theamount of PEI fraction and the thickness of the article as well asprocess conditions, including reagent concentration, agitation rate,temperature and the like, as will be recognized by those skilled in theart. The thus formed porous poly (aryl ether ketone) article is thenwashed with an alcohol, water, or other suitable solvent and dried.

PAEK substrates used to form composite membranes of this inventionexhibit a nanoporous surface. The nanoporous PAEK substrates arecharacterized by an asymmetric pore structure with smaller size surfacepores and larger size interior pores. The composite functionalizedseparation layer is formed at the surface layer. The surface layerexhibits a narrow pore size distribution with an average pore diameterbelow 70 nanometers, preferably between 20 and most preferably 5nanometers or below. The interior membrane pore structure exhibits poresize larger than the surface layer pore size, preferably the interiorbulk pore size being is larger than the average surface pore size by afactor of two or more. The PAEK substrates with interior pore structurethat combines mesopores and macropores are most suitable for thepreparation of high flux composite membranes. The thickness of thesurface layer is advantageously below 5 micron, preferably below 1micron and most preferably below 0.1 micron. The composite separationlayer is formed within the surface layer of the substrate or on top ofthe surface layer. For the asymmetric hollow fiber substrates, thesurface layer can be alternatively on the exterior surface or on theinterior bore side of the hollow fiber.

Formation of the functionalized PAEK membrane can be carried out via anumber of embodiments—(1) ketone groups on pore surfaces of thepreformed asymmetric porous PAEK substrate are functionalized, (2) thesurface of a dense PAEK substrate still containing the pore formingmaterial is functionalized followed by the removal of pore formingmaterial, or (3) the pore surface of an ultra-thin porous layer ofotherwise dense PAEK precursor is functionalized followed by the removalof pore forming material from the bulk of the porous substrate whereinan Janus type membrane is formed consisting of alternatingfunctionalized and virgin porous layers.

In one embodiment of the instant invention, the composite fluidseparation membrane is formed by a multi-step process: (a) a solid(non-porous) precursor article of a desired shape is formed from a poly(aryl ether ketone) polymer blend with a pore forming material, (b)benzophenone segments of poly (aryl ether ketone) polymer on the surfaceof the precursor shaped article are modified with functional groups, and(c) the solid poly (aryl ether ketone) precursor article is convertedinto a nanoporous membrane by removing the pore forming material.Preferred functional groups are selected from primary, secondary,tertiary or quaternary amine groups, carboxyl group, sulfonic acidgroup, phosphate group, primary, secondary or tertiary hydroxyl groups,ethylene oxide and sulfhydryl group. In a preferred embodiment, theshaped article undergoes crystallization following step (a) via asequence of solvent induced crystallization and thermal treatments.Alternatively, the article undergoes crystallization after surfacemodification step (b). The preferred article shape is the hollow fiberconfiguration and the preferred pore forming material is polyetherimide.

In another embodiment of the instant invention, the composite fluidseparation membrane is formed by a multi-step process: (a) a solid(non-porous) precursor article of a desired shape is formed from a poly(aryl ether ketone) polymer blend with a pore forming material, (b) thesurface of the solid poly (aryl ether ketone) precursor article isconverted into a thin nanoporous layer by removing the pore formingmaterial from the surface of the article to a predetermined depth, (c)the thus formed nanoporous layer is modified with functional groups viachemical modification of ketone groups in benzophenone segments of poly(aryl ether ketone) polymer, and (d) a porous composite membrane isformed by removing the remaining pore forming material from the interiorof the poly (aryl ether ketone) precursor article. In some embodimentsof the invention, steps (b) and (c) take place simultaneously. It iswithin the scope of the invention to crystallize the article followingstep (a) via a sequence of solvent and thermal treatments that generatesan asymmetric pore structure. The preferred article shape is the hollowfiber configuration and the preferred pore forming material ispolyetherimide. Preferred functional groups are selected from primary,secondary, tertiary or quaternary amino groups, carboxyl group, sulfonicacid group, phosphate group, primary, secondary or tertiary hydroxylgroups, ethylene oxide and suflydryl group. The nanoporous layer formedin step (b) exhibits an average pore size between 5 and 70 nm and thethickness of the porous layer formed in this step is preferably below 10micron and most preferably below 1 micron.

In another embodiment of the instant invention, the fluid separationmembrane is formed by a multi-step process: (a) a solid (non-porous)precursor article of a desired shape is formed from a poly (aryl etherketone) polymer blend with a pore forming material, (b) the article issubjected to a treatment step wherein poly (aryl ether ketone) polymerundergoes crystallization, (c) the solid poly (aryl ether ketone)precursor article is converted into a nanoporous substrate by removingthe pore forming material, and (d) the nanoporous substrate is modifiedwith functional groups to form a membrane. Preferably, thecrystallization of the poly (aryl ether ketone) polymer in the blendduring step (b) is carried out via a sequence of solvent and thermaltreatments that generates an asymmetric pore structure. The preferredarticle shape is the hollow fiber configuration and the preferred poreforming material is polyetherimide. Preferred functional groups areselected from primary, secondary, tertiary or quaternary amine groups,carboxyl group, sulfonic acid group, phosphate group, primary, secondaryor tertiary hydroxyl groups, ethylene oxide and sulfhydryl group. Thenanoporous layer of the membrane exhibits an average pore size between 5and 70 nm.

In one example, a nanoporous precursor article is prepared from a blendof PAEK polymer with a pore forming material (porogen). A precursornon-porous article is prepared from the PAEK/porogen blend by meltprocessing and is initially amorphous. The precursor amorphous articleundergoes crystallization by subjecting the article to a solventtreatment step. The solvent and the treatment conditions are selected toaffect crystallization of PAEK polymer phase in the article. Thecrystallization by the solvent treatment is carried out to limit thecrystallization to the surface region of the article only. The solventinduced crystallization is diffusion controlled. Thus, thedepth/thickness of the surface crystallized region can be controlled bythe duration of the treatment and temperature among other factors. Thesolvent treatment step is further followed by a thermal annealing step.The porogen acts as a pore forming material and is removed following thecrystallization step to provide the initial porous PAEK substratearticle. The porous surface of the article is modified by functionalgroups to form the fluid separation membrane. In some embodiments, thesurface functionalization is carried out following the thermal annealingstep and prior to the porogen removal step. In some embodiments, thesurface functional groups are further reacted with extender groups tomodify pore size and membrane surface characteristics.

In some embodiments, formation of the porous PAEK substrate and itssurface modification are carried out simultaneously. Namely, if theporous PAEK article is formed by the RPR process utilizing a primaryamine, the reaction can be carried out under conditions that affect boththe formation of the porous PAEK article and the modification of theporous PAEK article via ketimine group formation in a single stepprocess. Carrying out the RPR process at elevated temperatures,preferably above 80° C., most preferably from about 100° C. to about140° C., in an anhydrous reaction media while utilizing a highconcentration of a primary amine reagent, leads to the formation of aporous and functionally modified PAEK substrate in a single step. In onesuch example, a porous PEEK substrate is modified with ≈C═N—CH₂CH₂OHgroups in a single step process from PEEK/PEI blend by reacting theprecursor blend article with neat monoethanolamine at about 120° C. Theketimine group can be hydrolytically unstable. To improve hydrolyticstability the ketoimine group can be reduced using a mild reducing agentto form a stable secondary amine.

In some embodiments, it is desirable to form the initial porous PAEKarticles without affecting surface modification. The preformedunmodified nanoporous PAEK article is then modified in a following stepwith target functional groups. This enables preparation of PAEKmembranes tailored towards the target separation. To form an unmodifiedporous PAEK article by the RPR process, the precursor PAEK/PI blendarticle is contacted with a primary amine under conditions that suppressketimine group formation, i.e., at moderate temperatures and in arelatively dilute amine solution that preferably further contains water.It will be recognized by those skilled in the art that, by selectingbalanced reaction conditions, the PAEK modification via formation ofimine linkages can be largely suppressed while an adequately high rateof polyimide phase decomposition and removal is still maintained. Forexample, the RPR process can be carried out utilizingmonoethanolamine/dimethylformamide/water mixture 20/70/10 by volume at80° C., which provides for a porous PAEK article formation whilesuppressing functionalization via the imine group formation. However, ifthe ketimine groups were still formed during the RPR process they can beremoved in a subsequent step via hydrolysis.

The nanoporous PAEK membrane of this invention preferably has anasymmetric pore structure or a graded pore size distribution across thethickness of the porous wall. It is also within the scope of theinvention to have a combination of an asymmetric and graded poremorphology. In one example, the substrate wall is composed of distinctlayer regions of variable pore size and/or pore volume. It is preferableto form composite membranes utilizing a porous substrate with gradedpore size structure wherein the surface layer exhibits smaller averagepore diameter as compared to the interior pore size. One method offorming the multi-layer media of this invention is by coextrusion toform asymmetric pore configurations. Multilayer films or frits can bealso formed by compression molding or by calendaring together preformedsheets of variable PAEK composition. The preferred method of formingmultilayer substrates is by coextrusion. The method is particularlyuseful to form multilayer porous hollow fibers. The method provides forpreparation of substrates with 2 to 10, preferably 2 to 4, distinctlayers of variable blend composition and thus variable pore size andpore volume.

One preferred method of forming an asymmetric PAEK substrate is via thesequential crystallization process of the amorphous precursor. Thesurface of the shaped substantially amorphous PAEK/blend precursorformed by melt processing is treated initially by contacting with asolvent capable of crystallizing PAEK polymer phase. The crystallizationproceeds slowly as the solvent diffuses from the surface inwards. Thesolvent treatment time is controlled to affect surface layercrystallization to a desired depth only. After PAEK polymer in thesurface layer of the desired thickness is crystallized the process isterminated. The solvent treatment step is followed by a thermalannealing to complete the crystallization throughout the entiresubstrate material. Following the removal of the pore forming materialfrom the crystallized substrate an asymmetric morphology is formed witha surface layer containing substantially smaller size pores and with aninterior composed of larger size pores. In some embodiments, the initialPAEK precursor is a multilayer structure formed by coextrusion ofdifferent blend compositions. The sequential crystallization processaffects formation of an asymmetric layer in one of graded porositylayers formed by coextrusion.

The preformed shaped PAEK substrate is converted into a fluid separationmembrane tailored towards a specific application via surfacefunctionalization with target functional groups. The specificfunctionalization process methodology provides for membranes withdifferent separation characteristics. The following functionalizationapproaches are utilized: (1) The surface of an asymmetric nanoporousPAEK substrate is functionalized to form a surface separation layer of adesired pore size and functionality. The surface layer can be furthermodified via reaction with functional extender molecules. (2) Thesurface of as formed amorphous shaped PAEK blend precursor isfunctionalized with target functional groups. The article is subjectedto the crystallization step and the pore forming agent is removed. Thethus formed nanoporous composite PAEK membrane is formed with anultra-thin surface separation layer. The surface layer can be furthermodified via reaction with functional extender molecules. (3) The shapedamorphous precursor article is crystallized via a sequence of solventand thermal annealing steps. The surface is functionalized with targetfunctional groups. The pore forming material is removed and the articleis converted into a composite membrane with an ultrathin functionalizedsurface separation layer. The surface layer can be further modified viareaction with functional extender molecules. (4) The shaped amorphousprecursor article is crystallized via a sequence of solvent and thermalannealing steps. The pore forming material is removed from the surfaceof the substrate to a predetermined depth to form a thin porous layer.The porous surface layer is functionalized with target functionalgroups. The remaining pore forming material is removed from the interiorof the substrate and the article is converted into a composite membranewith an ultrathin functionalized surface porous separation layer. Thesurface layer can be further modified via reaction with functionalmolecules.

In one example, a hollow fiber is formed by coextruding two PAEK/PEIblends of different blend composition. After the PEI phase is removed, aporous substrate with two layers with distinctly different pore size andpore volume is formed. The surface layer with the smaller average poresize is functionalized to form the composite membrane. The asymmetricpore structure provides for a reduced resistance to fluid flow. It isalso within the scope of the present invention to form a substrate withmore than two layers that differ in pore size. The multi-layer poroussubstrate may contain porous layers that differ by at least about 10% inthe average pore size or by at least about 5% in the pore volume impartcertain advantages to the mechanical and functional characteristics ofthe membrane. For example, the multi-layer porous membrane can exhibitgood mechanical properties while providing a higher fluid flux. Themulti-layer porous substrate is preferably formed from two or morePAEK/polyimide blends that differ in blend chemical composition. Theblends can contain different PAEK polymers, different polyimide polymercomponents or can exhibit different PAEK/polyimide ratios. The PAEKpolymer content of the first blend can differ from the PAEK polymercontent of the second blend and any additional blends by between 5 to 50weight percent of PAEK polymer content, preferably by at least 10 to 25weight percent.

The multilayer substrate of the desired configuration can contain two,three or more contiguous layers that differ in the average pore sizeand/or pore volume. Furthermore, the individual layer can vary fromabout 5% of the overall wall thickness of the substrate to 50% of theoverall wall thickness of the substrate. The thickness of each layer canbe controlled and can be as thin as 10 micrometers. The layer with thesmaller size pores is positioned at the surface and is functionalized toform the separation layer.

It is important to functionalize PAEK membranes while minimizingreduction to crystalline structure. To maintain desired attributes likesolvent resistance the degree of crystallinity should be preferablyabove 20%, most preferably above 30%. The semi-crystalline nanoporousPAEK materials are highly solvent and temperature resistant.Nevertheless aggressive reaction conditions can proceed withmodification of both amorphous and crystalline regions leading to lossof mesoporous structure. Thus, the use of aggressive reaction conditionssuch as high reaction temperature, aggressive solvent media and reagentsin combination with excessive reaction time should be avoided to preventloss of crystalline phase. The use of mild reaction conditions enablesmodification of pore surfaces without affecting preformed porestructure, morphology and article's shape. It will be recognized bythose skilled in the art that a membrane with optimal separationproperties can be formed by modifying the PAEK substrate with functionalgroups appropriate to the synthetic scheme that will optimize thedesired pore size and functionality without materially affecting thedegree of crystallinity.

In preferred embodiments, the surface functional groups are formed bywet-chemical surface modification procedures on the pre-formed shapedPAEK article that serves as a substrate. The membrane formed via PAEKsubstrate surface modification can contain amine, carboxyl, acidchloride, aldehyde, isocyanate, ethylene oxide, sulfhydryl or hydroxylfunctional groups among others. It is within the scope of the inventionto covalently attach extender groups to the surface functional groups tofurther affect pore size and functionality. In one example, thefunctionalized porous PAEK substrate is reacted with a functionalmonomer that forms brush extender groups. The brush extender moleculesmodify the surface pore size to affect the separation efficiency. Brushextenders include low molecular weight hydrocarbons, oligomers orpolymers containing functional groups, such as epoxy groups or primaryamino-groups, ˜NH₂. Extender groups can be monofunctional ormulti-functional. In case of multi-functional extender groups one set offunctional groups is used to attach the brush to the functionalized poly(aryl ether ketone) surface. The attachment of the first targetedmulti-functional extender group molecules can be followed by reactingthe thus formed layer with an additional set of brush extendermolecule's to further affect pore size.

In some embodiments, functional groups on the PAEK substrate's surfaceare formed in a one-step direct chemical reaction or via a sequence ofchemical steps. For example, the PAEK articles prepared as describedabove can be modified by reducing surface ketone groups to form hydroxylgroups or by reacting ketone groups with multifunctional primary aminereagents via ketimine group formation to impart the target hydroxyl oramine group functionality.

In some embodiments, the PAEK substrate surface is modified first withreactive group intermediates converted to the target functionality in asubsequent step. Examples of such intermediate reactions may includesurface lithiation, nitration, aldehyde group attachment orchloromethylation to name a few. The modification of aromatic polymerswith these functional groups is generally known in the art and can bedeployed to functionalize PAEK substrate surfaces. Preferred reactivegroups used as intermediates for additional modification steps are aminoand hydroxyl groups.

The nanoporous PAEK substrates functionalized with hydroxyl, primaryamino groups or sulfhydryl groups are particularly preferred for thecomposite membrane preparation. The ═C═O ketone group in thebenzophenone PAEK polymer backbone, in particular, can be used to formfunctional groups on the PAEK substrate's surface. The highconcentration of ketone groups in poly (ether ketone) and poly (etherketone ether ketone ketone) polymers provide for a high concentration offunctional surface groups upon chemical modification.

The C═O ketone group in the PAEK backbone can be reduced to C—OH hydroxygroup. Thus, functionalized material can be used directly to formcomposite membranes with hydrophilic surface characteristics. In someembodiments of this invention, it may be desirable to react the hydroxylgroups with an additional brush extender group. The surface hydroxylgroups can be formed by reducing ketone groups on the surface of thePAEK substrate with a reducing reagent, such as sodium borohydride orlithium aluminum hydride. The surface hydroxyl groups can be furtherintroduced by forming ≈C═N—R—OH functional groups on the PAEK surfacevia reaction with primary amines containing hydroxyl groups wherein R isaliphatic or aromatic radical. In one example the ketone groups arereacted with monoethanolamine to form ≈C═N— CH₂— CH₂—OH functionalgroups. Direct reduction of ketone groups on the mesoporous surface ofPAEK to form diphenylmethanol functional units,

is particularly preferred. The formation of diphenylmethanol units inPEEK backbone is further illustrated schematically below:

The surface functionalization with —OH groups can be carried out on apreformed porous asymmetric PAEK membrane or utilizing a non-porousshaped PAEK article containing pore forming material followed by poreforming material removal to form the final asymmetric surfacefunctionalized membrane. It is desirable to conduct surfacefunctionalization without affecting crystalline phase. Loss ofcrystallinity during functionalization, including functionalization by—OH groups, can lead to a loss of preformed pore morphology. Loss ofcrystalline phase can further lead to the loss of solvent resistance.The functionalization via modification of ketone groups is best carriedout under reaction conditions that minimize chemical alteration ofcrystalline phase.

A number of reducing agents known in the art can be utilized includingNaAlH₄ and NaBH₄. Use of mild reducing agents such as NaBH₄ is preferredto preserve crystalline structure and pore morphology in preformedasymmetric PAEK membranes. The use of mild reaction conditions such asthe use of least aggressive solvents and modest reaction temperatures isfurther preferred. In some embodiments the surface functionalization ofnon-porous preformed PAEK articles can be carried out under moreaggressive conditions since the underlying pore morphology is formedfollowing functionalization. The preferred method of ketone groupreduction is the use of NaBH₄ reagent in isopropyl alcohol, IPA,solution or tetrahydrofuran, THF, solution that further containspolyethylene glycol, PEG, such as PEG 500. It was found surprisinglythat the addition of PEG provides for improved reaction conditions andconsumption of the reducing reagent.

The degree of substituting by functional groups can be controlled viareagent concentration, reaction conditions (in particular temperature)and reaction's duration. The formation of functional groups can befollowed by AT-FTIR spectroscopy, XPS spectroscopy or other methodsknown in the art. The AT-FTIR spectra of PEEK hollow fiber and PEEK-OHhollow fiber are shown in, respectively, FIGS. 1A and 1B. In the spectraof PEEK and PEK there are two peaks associated with carbonyl group; amain feature is the carbonyl asymmetric stretching peak at around 1644cm⁻¹ for both polymers, and the skeletal vibration at 1651 cm⁻¹ in PEEKand 1655 cm⁻¹ in PEK. The skeletal in-plane vibration of the phenylrings at 1498 cm⁻¹ is present in all PAEK polymers. Following surfacereduction, the concentration of ketone groups is reduced and isreflected by the reduction in the intensity of the peak at 1644 cm⁻¹.The change in the ratio of 1644 cm⁻¹ peak as related to the phenyl ringsat 1498 cm⁻¹ can be used to follow the progress of ketone groupreduction. The reduction of the ketone group is accompanied by theappearance of —OH stretching vibration in AT-FTIR spectra.

However, a quantitative determination of functional group concentrationby surface measurement methods can be difficult. The concentration of—OH groups in PAEK-OH materials can be measured quantitatively by UV-VISspectroscopy as follows: the PAEK-OH materials form a distinct red colorupon dissolution in concentrated sulfuric acid. Sulfuric acid isessentially the only solvent capable of dissolving semi-crystalline PAEKmaterials at room temperature. The color of PAEK-OH solutions isdistinctly different from the color of the unmodified material dissolvedin sulfuric acid. The UV-VIS spectra of both PEEK-OH and PEEK solutionsare shown in FIGS. 3A and 3B. The model compoundMBPPM-bis(4-(4-methoxyphenoxy)phenyl)methanol dissolved in sulfuric acidwas used to measure the concentration of —OH groups in functionalizedPEEK materials. Model compound MBPPM was synthesized and the solution ofMBPPM in sulfuric acid was used to construct a calibration curve usingthe absorption peak at 508 nm. The UV-VIS spectra of MBPPM dissolved insulfuric acid and the calibration curve are shown in FIGS. 4A and 4B,respectively. The calibration curve was used to measure concentration of—OH groups in mesoporous PEEK membranes functionalized under differentprotocols.

The UV-VIS method of measuring hydroxyl group concentration is highlysensitive and allows determination of the concentration of —OH groups insurface functionalized PEEK-OH materials. The method enablesoptimization of reaction conditions to control the degree of surfacefunctionalization and the depth of the functionalized surface layer. Theconcentration of functional groups can be measured as a function of timeand represented as a weight concentration (mmol/g units) or as a surfacegroup concentration (μmmol/cm² units). High concentration of surfacegroups can be attained in a short reaction duration time. Theconcentration of surface groups above 1×10⁻⁵ μmol/cm² is preferred, mostpreferred is surface group concentration above 5×10⁻⁵ μmol/cm².

The porous structure of functionalized PEEK-OH materials was furtherevaluated using nitrogen adsorption BET measurements. The degree ofcrystallinity of porous PEEK-OH materials was further evaluated byDifferential Scanning calorimetry (DSC). The measured heat of fusion wasused to calculate the degree of crystallinity. Modification protocolswere optimized to attain consistent and controlled modification of thesubstrate while minimizing changes to the mesoporous pore morphology anddegree of crystallinity.

The porous PAEK substrate functionalized with hydroxyl groups can befurther converted to the desired new functionality through chemicaltransformations of —OH groups. For example, the surface of porous PAEKarticles can be functionalized with carboxylic groups utilizing a commonkey-intermediate, the PAEK-OH functionalized material. The latter isobtained by surface reduction of ketone groups in benzophenone linkage.Substitution of the hydroxyl groups, under mild acidic conditions, with4-ammobenzoic acid and succinamic acid provides for PAEK-Ph-COOH andPAEK-(CH₂)₂—COOH functionality. The PAEK-OH functionalized material canbe reacted with a sultone, for example 1,4-butane sultone, under basicconditions to form sulfonic acid functionalized surface.

A broad method of PAEK substrate functionalization is via reaction ofthe ketone group in PAEK backbone with a functional hydrocarboncontaining a primary amino group. In this embodiment, the ketone groupsin poly (aryl ether ketone) backbone are reacted with a low molecularweight hydrocarbon, oligomer or a polymer containing primaryamino-functional groups ˜NH₂ and additional functional groups thataffect separation characteristics of the separation layer. Theattachment of the target molecule to the substrate is thus carriedutilizing the primary amino group and is completed via the ketiminegroup formation. In some embodiments, this reaction is followed by theketimine group reduction to form a durable covalent bond of moleculescontaining functional groups attached to the PAEK surface separationlayer.

The attachment of a functional hydrocarbon molecule to the PAEKsubstrate's surface layer via formation of the ketimine linkage isfurther illustrated below:

wherein R is a low molecular weight hydrocarbon, oligomer or a polymercontaining primary amino-functional groups —NH₂ and at least oneadditional functional group, such as hydroxyl group, amino group,carboxyl group or sulfhydryl group, wherein R is an aliphatic, aheterocyclic or an aromatic radical. Difunctional and multifunctionalamines are particularly preferred. Examples of difunctional aminesinclude ethylenediamine, propylenediamine, iso-butylenediamine,1,4-diaminobutane, diethylenetriamaine, tetraethylenepentamine,ethylethanolamine, diaminocyclohexane, phenylenediamine, toluenediamine.R radical can contain multiple amino groups to provide PAEK separationlayer with a high concentration of functional groups. Moleculescontaining a high concentration of primary amino groups are particularlypreferred. Polyvinylamine, polyethylene imine or poly (ethylene glycol)diamine of controlled molecular weight are utilized to form theseparation layer on the surface of PAEK substrate with a controlledmolecular weight cutoff and pre-determined functionality. Poly (ethyleneglycol) diamine of the general formula

is used to form separation layers with antifouling characteristics,wherein n can range from 3 to 12. PAEK media with PEG-NH₂ functionalitycan be reacted with functional molecules in a following step to furthermodify separation layer pore size and functionality.

In some embodiments, the H₂N—R molecule containing hydroxyl functionalgroups, rather than an additional amino group, is utilized. Hydroxylgroups functionalize the separation layer an impart hydrophilic surfaceproperties. R radicals containing tertiary, secondary or primary alcoholgroups are attached to the PAEK porous surface via the Schiff baseketimine linkage formation (R is an aliphatic, an aromatic orheterocyclic hydrocarbon radical). The R radical can further containmultiple hydroxyl groups. In some embodiments, it is desirable to reducethe ketimine linkage to form a secondary amine. The secondary aminegroup is hydrolytically more stable. In some embodiments, the secondaryamine group is further alkylated to form a tertiary amine.

The functionalization of PAEK media surface with ≈C═N—CH₂CH₂OH groupscan be carried out by reacting ketone groups in the PAEK backbone withmonoethanolamine. This can be conveniently carried out during a RPRprocess wherein the porous structure and functionalization take placesimultaneously. Alternatively, the pre-formed mesoporous PAEK is reactedwith monoethanolamine in a separate step. Other aliphatic aminofunctional alcohols, such as diethanolamine, propanolamine,dipropanolamine, or 4-amino-1-butanol, can be utilized. One preferredH₂N—R—OH linker molecule is amino functionalize poly (ethylene glycol).The H₂N—R—OH molecules containing aromatic rings is another class offunctional groups.

Preparation of amino functional media via Schiff base linkage in someembodiments is followed by the ketimine group reduction. In the firststep, the porous PEEK is reacted with a difunctional hydrocarbonradical, H₂N—R—NH₂. In the second step, the ketimine group is reducedusing a reducing agent such as sodium cyanoborohydride, NaBH₃CN, to formPEEK—NH—R—NH₂ functionalized surface. R is an aromatic, heterocyclic oraliphatic radical that can contain additional functional groups.

In another preferred embodiment of the invention, the polymer backbonein the mesoporous PAEK substrate is modified to form benzhydrylaminefunctional

units on the PAEK surface Multiple methods of forming functionalbenzhydrylamine groups via modification of benzophenone are known in theart. In some approaches, multiple reaction steps are used to form thebenzhydrylamine functionality. In one method, the porous substrate isreacted first with the hydroxyamine to form oxime intermediate. In thesecond step, the oxime is reduced with LiAIH₄ to form benzhydrylamine.However, the formation of some secondary amine can take place as a sidereaction. In another method, the porous substrate is reacted first withNaBH₄ to form the diphenyl methanol unit which is followed by reactingthe diphenyl methanol with HBr. In the next step, the substrate isreacted with ammonia to form benzhydrylamine functionality. This methodinvolves a large number of steps and can generate surface crosslinking.In a further method, the porous substrate is reacted first with theHCO₂NH₄ to form diphenylformamide. In the second step, the formamide ishydrolyzed with strong HCl to form benzhydrylamine groups. This methodis a modification of the Leuckart reaction and is preferred.

To form benzhydrylamine functionality following the Leuckart method, theporous PAEK substrate is reacted with the ammonium formate at 170° C.for 4 hours under argon (ammonium formate boils at 180° C.). The porousPAEK media is highly temperature and solvent resistant and harshconditions can be implemented without a major effect on the porousstructure. The porous media is washed extensively with water to removedecomposition products of HCO₂NH₄ that may include ammonia andformamide. In the final step, the porous article is treated with 1N HClto convert diphenylformamide into protonated benzhydrylamine groups andwashed with water. The HCl is removed by washing with a dilute NaOHsolution, followed by washing with water and the final functionalizedsubstrate dried under argon.

The porous functionalized PAEK membranes prepared as described above canbe further reacted with functional monomers to modify membraneseparation characteristics further. The functional groups on PAEK porousmembrane surface are used to covalently attach hierarchically a new setof functional groups to the surface of the PAEK substrate to formnanoporous composite membranes with progressively lower molecular weightcut off characteristics. The porous PAEK substrate functionalized withprimary amino groups is further modified by reactions with functionalmonomers or brush extender groups. Multifunctional monomers containingacid chloride, isocyanate and epoxy groups are particularly preferred.In one example, the separation layer is formed on the surface of thePAEK substrate via the flowing sequence of reaction steps: (a) formingfunctional groups on the surface of PAEK substrate, (b) reacting thusformed functional groups with a multifunctional monomer A and (c)reacting the surface modified with monomer A with a multifunctionalmonomer B. In some embodiments, both monomers can be a mixture ofmonomers and are applied from solutions by a wet chemistry process. Themultifunctional monomer A has a general formula R(X)_(n) wherein R is anorganic moiety selected from aromatic, aliphatic, alicyclic orheterocyclic groups and combinations thereof; X is a functional groupselected from a primary or secondary amino group, acid chloride group,hydroxyl group, sulfhydryl group, aldehyde group, epoxy group orisocyanate group; n represents an integer of 2 or more. In someembodiments, the functional group is part of the heterocyclic radical.The multifunctional monomer B has a general formula R′(Y)_(n) wherein R′is an organic moiety selected from aromatic, aliphatic, alicyclic orheterocyclic groups and combinations thereof; Y is a functional groupselected from a primary or secondary amine group, acid chloride group,hydroxyl group, sulfhydryl group, aldehyde group, epoxy group orisocyanate group; n represents an integer of 2 or more. In someembodiments, the functional group is part of the heterocyclic radical.The functional groups of the substrate, the monomer A and the monomer Bare selected to form covalent bonds. In a most common embodiment, thePAEK surface is functionalized with primary amine or hydroxyl groups,the functional group of monomer A is an acid chloride group, —COCl, oran epoxy group and the functional group of the monomer B is a primary orsecondary amino group, —NH₂, ═NH. The functionalized separation layerexhibits a narrow pore size distribution with an average pore diameterbelow 50 nm, preferably below 10 nm. In embodiments directed to the ROseparation process, the pore size is below 0.2 nm.

The amine group functionalized PEEK hollows are particularly useful forhierarchical sequential additional surface modification to controlmembrane molecular weight cut off. In one example, the aminefunctionalized hollow fiber is modified via sequential exposures totrimesoyl chloride, TMC, and meta phenylenediamine, MPD. The aminefunctionalized PAEK substrate was reacted first with the carboxylic acidchloride functionality of TMC in a reticulate synthesis. In thefollowing step, the carboxylic acid chloride functionality of themodified substrate is reacted with amine functional groups of MPD. Amembrane module is constructed utilizing amine functionalized PEEKhollow fibers. The solution of reactants and washing fluids isintroduced on the bore side of hollow fibers through the feed side portof the module. The reservoir containing solutions of reactants andwashing fluids were maintained under argon. Dilute solutions of TMC intoluene and MPD in toluene (0.05M) are prepared for the two reactionsteps in the deposition cycle. Dry toluene and acetone solutions areprepared for rinse steps in the deposition cycle. In the first step, thePEEK substrate surface is contacted with the dilute TMC solution intoluene which reacts with pendant amino groups. The solution isintroduced into hollow fiber bores and after 20 s of exposure time, thesolution is removed, replaced by toluene and the substrate rinsed withtoluene. The excess of toluene is removed under a flow of argon. At thisstage of the cycle, the surface contains an excess of unreacted acidchloride groups. In the following half cycle, the PEEK substrate surfaceis further reacted with the dilute MPD solution in toluene for 20 s. Thesolution is removed, replaced by acetone and the substrate washedextensively with acetone to remove any excess of MPD. At the end of thefirst complete cycle, the substrate surface contains an excess of aminegroups that are reactive to TMC. The reticular synthesis and thedeposition cycles can be continued. The number of reticulate cyclesaffects membrane properties. The process is stopped after a membranewith a desired molecular weight cut off is formed. Depending on themonomer composition of the last solution used in the cycle (TMS or MDA),the surface of the composite layer will have an excess of amino or acidchloride groups. Carboxylic acid groups are formed upon hydrolysis ofacid chloride groups. The presence of these functional groups cancontribute to the tailored separation properties of the membrane. Toimpart antifouling properties to the membrane, an additional distinctlayer can be formed on the surface. To provide anchoring sites for thislayer formation, the TMC solution is used as the terminal step in thecycle. The acid chloride groups on the surface of the composite layerare reacted with the amino-functional polyethylene oxide to form theanti-fouling layer.

It is within the scope of the invention to covalently attach extendergroups to the surface functional groups to further affect pore size andfunctionality. In this step, the porous PAEK substrate functionalizedwith hydroxyl or primary and secondary amino groups is reacted withbrush extender groups. The brush extender molecules modify the surfacepore size to affect the separation efficiency. Brush extenders includelow molecular weight hydrocarbons, oligomers or polymers containingfunctional groups, such as epoxy groups, acid chloride groups orisocyanate groups. Extender groups can be monofunctional ormulti-functional. In case of multi-functional extender groups one set offunctional groups is used to attach the brush to the functionalized poly(aryl ether ketone) surface. The attachment of the first targetedmulti-functional extender group molecules can be followed by reactingthe thus formed layer with an additional set of brush extendermolecule's to further affect pore size.

Ethylene oxide, propylene oxide and butylene oxide oligomers areparticularly preferred as brush extender molecules due to theirantifouling characteristics. Extender groups can be monofunctional ormulti-functional. Multifunctional brush extender molecules containingepoxy functional groups are particularly preferred. These include poly(ethylene glycol) diglycidyl ethers of different molecular weights,trimethylolpropane triglycidyl ether, tris(4-hydroxyphenyl)methanetriglycidyl ether, glycerol diglycidyl ether, resorcinol diglycidylether, bisphenol A diglycidyl ether available commercially as DER™ 332,commercially available tetraphenolethane tetraglycidylether (EPON™ Resin1031) and mixtures thereof. The reaction of surface hydroxyl groups withepoxy functional oligomers can be complicated by the competition of thenew hydroxyls formed during initial reaction further reacting with thestarting epoxide. Tertiary amines are used to catalyze the reaction. Amixture of oligomers that differ in functionality can be furtherutilized.

A broad range of solvents can be utilized in the functionalizationprocesses. The semi-crystalline structure of the PAEK substrate makes itsolvent resistant. Mild swelling may take place in contact with certainaggressive solvents. Aromatic, aliphatic and chlorinated hydrocarbons,aprotic solvents, ethers, alcohols and ketones can be used in theseparation layer functionalization reactions as long as the solventmedia is not reactive towards reactants. Extensive washing is requiredafter each reticulate synthetic step to remove unreacted monomers.

The PAEK substrate configurations are highly flexible and can bepackaged into membrane filter reaction vessels. In these vessels, thesubstrate is easily accessible to reactants. The PAEK substrate ispackaged into a permanent or a temporary housing to carry out theseparation layer functionalization. The housing assembly is configuredto house flat sheet, such as spiral wound, hollow fiber, or monolithconfigurations with the hollow fiber configuration preferred. Thehousing can be jacketed to carry out reactions at a controlledtemperature. PAEK hollow fibers are sealed within the housing by formingfluid tight tubesheets. The tubesheets are formed by utilizing thermosetor thermoplastic potting materials. Commercial hollow fiber devicestypically contain thousands of hollow fibers. The PAEK initial surfacefunctionalization and/or any subsequent additional modifications can becarried out on the lumen or shell side of hollow fibers. The preformedporous or dense precursor hollow fibers are utilized followingprocedures described above. Reactants and wash solutions are introducedvia the feed port of the housing. The port is connected to a pump oranother delivery system to introduce and transport reactants throughhollow fibers. The liquid flow rate is controlled to allow foracceptable yield during each reaction step and to reduce reactantwastage. Optionally, the progress of the reaction is monitoredcontinuously by measuring reactant concentration in the exit waste line.The reactant delivery rate can be adjusted to reduce bypass andunderutilization of reactants. Upon the completion of each reaction stepthe process is switched to the next step.

The separation layer functionalization can be further carried out byimmersing the precursor PAEK substrate into the reaction media orcontinuously transporting the substrate through the reaction media. Toattain optimal PAEK material surface modification or to improve theefficiency of the modification process, the reaction advantageously iscarried out in anhydrous conditions and/or at an elevated temperature.The PEAK substrates are highly temperature and solvent resistant. Thereaction temperature during the synthesis can be between 20° C. to 150°C.

The composite poly (aryl ether ketone) membranes of this invention areformed with separation layers of controlled pore size and functionalitythat in turn address a broad range of fluid separation applications. Theapplications may include well-established ultrafiltration (UF),nanofiltration (NF) and reverse osmosis (RO) processes. Emergingapplications such as organic solvent nanofiltration and the separationand recovery of active pharmaceutical ingredients, APIs, from organicsolvent media can be further efficiently addressed by membranes of thisinvention.

The present invention is described below by examples, which should notbe construed as limiting the present invention.

EXAMPLES Example 1

This example describes the preparation of the nanoporous composite PEEKmembrane functionalized with hydroxyl groups. Poly (ether ether ketone)and polyetherimide, PEEK/PEI, blend (PEEK, Victrex 381G and PEI Ultem1000; 50:50 by weight) was compounded in a twin extruder. A precursorhollow fiber 550 micron outside diameter and 300 micron inside diameterwas prepared by melt extrusion at circa 380° C. and quenched in water.The hollow fiber was substantially amorphous. The exterior surface ofthe hollow fiber was washed with hexane, followed by a butanol solventtreatment at 100° C. for 20 min. The solvent treatment is directed toaffect surface crystallization. The hollow fiber was then heat treatedat 300° C. for 0.5 hour to affect the crystallization of the PEEKpolymer in the bulk wall. The hollow fiber was immersed intoNMP/monoethanolamine/water solution 80/10/10 by volume at 80° C. for 15min. The reservoir containing the solution was blanketed with nitrogen.The hollow fiber was removed from the solution and thus formed poroussurface layer of the hollow fiber was washed extensively with waterfollowed by isopropanol and acetone. The hollow fiber was then dried at80° C. overnight. The treatment formed a thin surface porous layer withdense hollow fiber wall interior. At this intermediate stage of membranepreparation the hollow exhibits porous exterior surface layer with densenon-porous interior. The SEM microphotograph of hollow fiber crosssection and hollow fiber crossection with exterior layer stained witheosin dye are shown in FIGS. 5A and 5B, respectively. The pre-driedhollow fiber was treated with 1.0% w/v sodium borohydride solution inTHF/PEG (1:1 ratio) for 4 hours while maintaining the solution at 50° C.The hollow fiber was then washed sequentially with dilute HCl solution(0.1N) and distilled water and then dried under nitrogen at 80° C. to aconstant weight. The surface functionalized hollow fiber was immersedinto NMP/monoethanolamine/water solution 80/10/10 by volume at 80° C.for 24 hours to complete removal of PEI phase from the hollow fiber wallinterior. The reservoir containing the solution was blanketed withnitrogen. The hollow fiber was removed from the solution and washedextensively with water followed by isopropanol and acetone. The hollowfibers were then dried at 80° C. overnight. The thus prepared compositehollow fiber membrane consisted of a thin surface layer functionalizedwith hydroxyl groups (estimated average pore size 14 nm diameter) withthe interior bulk wall porosity unaffected by the functionalization (theestimated pore size as measured BET nitrogen adsorption was 32 nmaverage pore diameter). The surface of the modified hollow fiber wasfound to be highly hydrophilic and easily wetted with water. The surfacecharacteristics of thus formed hollow fiber were evaluated usingATR-FTIR. ATR-FTIR spectra showed a significant reduction of >C═O groupconcentration (residual absorption of y C═O at 1640 cm⁻¹ and 1597 cm⁻¹)and a high concentration of —OH groups attributed to the benzhydrolmoiety of thus functionalized PEEK was detected (y O—H peak at 3400cm⁻¹). The separation characteristics of the hollow fiber membrane wereevaluated by conducting an ultrafiltration test utilizing polystyrene,PS, solution in ethyl acetate MW 100,000. Concentrations of PS-solutionswere determined with a UV/Vis scanning spectrophotometer at a wavelengthof 260 nm. The retention of PS was 99%.

Example 2

This example describes the preparation of the nanoporous composite PEEKmembrane surface functionalized with hydroxyl groups. Poly (ether etherketone) and polyetherimide, PEEK/PEI, blend (PEEK, Victrex 381G and PEIUltem 1000; 50:50 by weight) was compounded in a twin extruder. Aprecursor hollow fiber 500 micron outside diameter and 300 micron insidediameter was prepared by melt extrusion at circa 380° C. and quenched inwater. The hollow fiber was substantially amorphous. The exteriorsurface of the hollow fiber was washed with hexane, followed by acetonesolvent treatment at 50° C. for 20 min. The solvent treatment isdirected to affect surface crystallization. The hollow fiber was thenheat treated at 310° C. for 0.5 hour to affect the crystallization ofthe PEEK polymer in the bulk wall. The hollow fiber was treated with1.0% w/v sodium borohydride solution in THF/PEG (1:1 ratio) for 4 hourswhile maintain the solution at 80° C. The hollow fiber was then washedsequentially with dilute HCl solution (0.1N) and distilled water andthen dried under nitrogen at 80° C. to a constant weight. The surfacefunctionalized hollow fibers were immersed intoNMP/monoethanolamine/water solution 80/10/10 by volume at 80° C. for 24hours. The reservoir containing the solution was blanketed withnitrogen. Hollow fibers were removed from the solution and washedextensively with water followed by isopropanol and acetone. Hollowfibers were then dried at 80° C. overnight. The thus prepared compositehollow fiber membrane consisted of an ultra-thin surface layerfunctionalized with hydroxyl groups (estimated average pore size 11 nmdiameter) with the interior bulk wall porosity unaffected by thefunctionalization (estimated average pore size 35 nm diameter). Thesurface of the modified hollow fiber was found to be highly hydrophilicand easily wetted with water. The surface characteristics of thus formedhollow fiber were evaluated using ATR-FTIR. ATR-FTIR spectra showed asignificant reduction of >C═O group concentration (residual absorptionof y C═O at 1640 cm⁻¹ and 1597 cm⁻¹) and a high concentration of —OHgroups attributed to the benzhydrol moiety of thus functionalized PEEKwas detected (y O—H peak at 3400 cm⁻¹). The separation characteristicsof the hollow fiber membrane were evaluated by conducting anultrafiltration test utilizing polystyrene, PS, solution in ethylacetate MW 100,000. Concentrations of PS-solutions were determined witha UV/Vis scanning spectrophotometer at a wavelength of 260 nm. Theretention of PS was 99%.

Example 3

Composite hollow fibers were prepared as described in Example 2 exceptthat the reaction time of ketone group reduction was varied. Theconcentration of hydroxyl groups as a function of the reaction time wasmeasured by dissolving functionalized hollow fibers in concentratedsulfuric acid. The PEEK-OH forms a carbo-cation upon dissolution issulfuric acid as shown in FIG. 2 . The PEEK-OH solution in sulfuric acidas well as the solution of reference precursor PEEK hollow fiber areshown in FIGS. 3A and 3B. Absorption peak intensity at 508 nm wasmeasured in UV-VIS spectra. An example of UV-VIS spectra are shown inFIG. 4A. The calibration curve (shown in FIG. 4B) was constructed usingmodel compound bis(4-(4-methoxyphenoxy) phenyl) methanol, BMPPM.

The results are summarized in Table 1.

Reaction time point Hydroxyl group concentration (min) C(mmol/g) T2-20min 4.82E−04 T3-40 min 1.68E−03 T4-90 min 4.50E−03 T5-180 min  7.43E−03The degree of surface functionalization increases with increase inreaction time. Reaction conditions can be used to control the degree offunctionalization. Extensive reaction times lead to an increase in thethickness of the functionalized layer.

Example 4

This example describes the preparation of the nanoporous composite PEEKmembrane surface functionalized with amino groups. Poly (ether etherketone) and polyetherimide, PEEK/PEI, blend (PEEK, Victrex 381G and PEIUltem 1000; 50:50 by weight) was compounded in a twin extruder. Aprecursor hollow fiber 550 micron outside diameter and 300 micron insidediameter was prepared by melt extrusion at circa 380° C. and quenched inwater. The hollow fiber was substantially amorphous. The exteriorsurface of the hollow fiber was washed with hexane, followed by abutanol solvent treatment at 100° C. for 20 min. The solvent treatmentis directed to affect surface crystallization. The hollow fiber was thenheat treated at 310° C. for 0.5 hour to affect the crystallization ofthe PEEK polymer in the bulk wall. The hollow fiber was immersed intoNMP/monoethanolamine/water solution 80/10/10 by volume at 80° C. for 15min. The reservoir containing the solution was blanketed with nitrogen.The hollow fiber was removed from the solution and thus formed thinporous surface layer of the hollow fiber was washed extensively withwater followed by isopropanol and acetone. The hollow fiber was thendried at 80° C. overnight. The hollow fiber was placed into a reactionvessel equipped with a Dean-Stark trap and a reflux system. A solutionconsisting of 25 g ammonium formate, 30 ml formamide, 20 ml 88% formicacid and 100 ml nitrobenzene was placed into the reaction vessel purgedwith nitrogen and the temperature increased incrementally to distill thewater. The temperature was raised and maintained at 165° C., for 2hours. The solution was brought to room temperature and the hollow fiberremoved. The hollow fiber rinsed sequentially with ethanol,dichloromethane and ethanol. The modified porous PEEK was deformylatedby hydrolysis for 60 min with solution comprised of 12 M HCl:C₂H₅OH(1:1) at temperature of 65° C. The amine hydrochloride modified hollowfibers were washed sequentially with ethanol, dichloromethane andmethanol, and dried. The amine hydrochloride functionalized PEEK wasevaluated by ATR-FTIR. The spectrum showed a new band in the 3000 cm⁻¹region attributed to amine functional groups. The surface functionalizedhollow fiber was immersed into NMP/monoethanolamine/water solution80/10/10 by volume at 80° C. for 24 hours. The reservoir containing thesolution was blanketed with nitrogen. This completed the removal of thePEI phase from the interior wall of hollow fibers. Hollow fibers wereremoved from the solution and washed extensively with water followed byisopropanol and acetone. Hollow fibers were then dried at 80° C.overnight. The thus prepared composite hollow fiber membrane consistedof a thin surface layer functionalized with primary amine groups(estimated average surface pore size 14 nm diameter) with the interiorbulk wall porosity unaffected by the functionalization (estimatedinterior wall average pore size 32 nm diameter). When subjected to theKaiser ninhydrin test, the benzhydryl amine functionalized PEEK gave ablue color after 30 sec at 25° C. The surface of the modified hollowfiber membrane was found to be highly hydrophilic and easily wetted withwater. The surface characteristics of thus formed hollow fiber wereevaluated using ATR-FTIR. Adsorption in the 3300-3000 cm⁻¹ region wasattributed to the presence of —NH₂ groups. The separationcharacteristics of the hollow fiber membrane were evaluated byconducting an ultrafiltration test utilizing polystyrene, PS, solutionin ethyl acetate MW 100,000. Concentrations of PS-solutions weredetermined with a UV/Vs scanning spectrophotometer at a wavelength of260 nm. The retention of PS was 96%.

Example 5

This example describes preparation of a composite PEEK membrane with aseparation layer modified towards a lower molecular weight cut off. Thecomposite hollow fiber membrane prepared as described in Example 1 wasreacted with the epoxy-functional polyethylene oxide oligomer, poly(ethylene glycol) diglycidyl ether MW 6000, to modify the surface poresize of the membrane. The polyethylene oxide groups are known to impartanti-fouling characteristics. The hollow fiber was contacted with 5%solution of diglycidyl ether in THF at reflux conditions for 4 hours.The solution further contained 0.1% ofN,N,N′,N′-tetramethyl-1,6-hexanediamine, TMHD, catalyst. The separationcharacteristics of the hollow fiber membrane were evaluated byconducting an ultrafiltration test utilizing polystyrene, PS, solutionin ethyl acetate MW 13,000. Concentrations of PS-solutions weredetermined with a UV/Vs scanning spectrophotometer at a wavelength of260 nm. The retention of PS was 97%.

While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

1-29. (canceled)
 30. A system for separating a fluid mixture into afraction enriched in at least one component and a fraction depleted inthe at least one component, said system comprising: an asymmetricsurface functionalized poly (aryl ether ketone) fluid separationmembrane formed according to the method of claim 32; and a source ofpressure for maintaining a pressure difference, or in case of a vaporcomponent a partial pressure difference, across the fluid separationmembrane, whereby the fraction enriched in the at least one componentand the fraction depleted in the at least one component are generated bypreferentially permeating a portion of the fluid mixture through thefluid separation membrane.
 31. The system of claim 30 wherein the fluidmixture is an organic solvent-based fluid mixture.
 32. A method offorming a composite fluid separation membrane, said method comprisingthe steps of: (a) forming a blend of a poly(aryl ether ketone) polymerwith a polyimide; (b) forming a shaped article from the blend by meltprocessing, wherein the article is substantially amorphous; (c)subjecting a surface of the article to a solvent treatment step thatinduces crystallization in the article to a predetermined depth; (d)subjecting the article, subsequent to step (c), to a secondcrystallization step to complete crystallization; (e) introducingfunctional groups on the surface of the article; (f) bringing thearticle into contact with a solution of primary amine or hydrazine toaffect decomposition of the polyimide; and (g) removing products ofpolyimide decomposition from the article.
 33. A method of forming acomposite poly (aryl ether ketone) membrane, said method comprising thesteps of: (a) forming a blend of a poly(aryl ether ketone) polymer witha polyimide; (b) forming a shaped article from the blend by meltprocessing, wherein the article is substantially amorphous; (c)subjecting a surface of the article to a solvent treatment step thatinduces crystallization in the article to predetermined depth; (d)subjecting the article, subsequent to step (c), to a thermal annealingstep to complete crystallization; (e) removing the polyimide from thesurface of the article to a predetermined depth to form a mesoporouslayer; (f) introducing functional groups on a surface of the mesoporouslayer via reaction with benzophenone segments of a polymeric backbone ofthe polymer; (g) bringing the article into contact with a primary amineor hydrazine to affect decomposition of the polyimide; (h) removingproducts of polyimide decomposition from the article; and (i) recoveringthe composite membrane, wherein only the surface of the mesoporous layeris functionalized.
 34. The method of claim 32 wherein the functionalgroups on the surface of the article are introduced via reaction withbenzophenone segments of a polymeric backbone of the poly(aryl etherketone) polymer.
 35. The method of claim 32 wherein following step (e)or step (g) the functional groups on the surface of the article arereacted with functional organic molecules to form a separation layercovalently attached to the surface of the article via the functionalgroups.
 36. The method of claim 32 wherein the crystallization in step(c) is carried out in an alcohol, a ketone, a chlorinated hydrocarbon,polyethylene glycol, an aromatic hydrocarbon or a mixture thereof. 37.The method of claim 36 wherein the ketone is an acetone, a methyl ethylketone, a 2-hexanone, an isophorone, a methyl isobutyl ketone, acyclopentanone, an acetophenone, a valerophenone, a pentanone or amixture thereof or a mixture with water.
 38. The method of claim 32wherein the crystallization to the predefined depth in step (c) definesa surface layer that is mesoporous.
 39. The method of claim 38 wherein athickness of the mesoporous surface layer is less than 1 micron.
 40. Themembrane of claim 38 wherein the functional groups are further reactedwith functional organic molecules to form a separation layer covalentlyattached to the mesoporous surface layer of the membrane.
 41. The methodof claim 40 wherein the separation layer has a concentration offunctional groups of at least 1×10⁻⁵ μmol/cm².
 42. The method of claim41 wherein the separation layer has a concentration of functional groupsof at least 5×10⁻⁵ μmol/cm².
 44. The method of claim 32 wherein thefunctional groups are selected from: primary, secondary, tertiary orquaternary amine groups, a carboxyl group, a sulfonic acid group, aphosphate group, primary, secondary or tertiary hydroxyl groups, anethylene oxide group and/or a sulfhydryl group.
 44. The method of claim32 wherein the fluid separation membrane is in the shape of a film, afrit, a hollow fiber or a monolith.
 45. The method of claim 32 whereinthe fluid separation membrane is an ultrafiltration, nanofiltration orreverse osmosis membrane.
 46. The method of claim 32 wherein the poly(aryl ether ketone) comprises a poly (ether ketone), a poly (ether etherketone), a poly (ether ketone ketone), a poly (ether ether ketoneketone) or a poly (ether ketone ether ketone ketone).
 47. The method ofclaim 32 wherein the polyimide is a mixture of polyimides or a mixtureof a polyimide with an additional pore-forming material.
 48. The methodof claim 32 wherein the polyimide is a poly (ether imide).
 49. Themethod of claim 32 wherein a concentration of the functional groups isat least 1×10⁻⁵ μmol/cm².
 50. The method of claim 49 wherein theconcentration of functional groups is at least 5×10⁻⁵ μmol/cm².
 51. Themethod of claim 32 wherein the article is mesoporous with a surfacelayer exhibiting an average pore diameter smaller by at least factor oftwo than an average pore diameter of an interior of the article.
 52. Themethod of claim 51 wherein the average pore diameter of the surfacelayer is less than 70 nm.
 53. The method of claim 52 wherein the averagepore diameter of the surface layer falls within the range of 5 nm to 20nm.
 54. The method of claim 32 wherein the fluid separation membrane hasa pore volume between 40 and 80%.
 55. The method of claim 32 wherein thefluid separation membrane exhibits a degree of crystallinity of at least20%.
 56. The method of claim 32 wherein the crystallization in step (d)is carried out by a thermal treatment at a temperature between 210° C.and 310° C.
 57. The method of claim 34 wherein the functional groups areformed by reduction of ketone groups in a benzophenone segment of thepolymeric backbone to hydroxyl groups.
 58. The method of claim 57wherein the ketone group reduction is carried out utilizing sodiumborohydride solution in an alcohol/water solvent mixture, or analcohol/polyethylene glycol solvent mixture or atetrahydrofuran/polyethylene glycol solvent mixture.
 59. The method ofclaim 57 wherein the hydroxyl groups are further reacted with functionalepoxide molecules.